The present invention relates to a method enabling a plurality of transponders present simultaneously in the field of analysis apparatus to be identified, and also to analysis apparatus and to a set of transponders for implementing such a method.
Numerous analysis apparatuses are known that enable a transponder to be identified for example to control access to a building.
Most such analysis apparatuses are adapted to identify only a small number of transponders at a time, which is not a problem when controlling access to a building since the number of people, and thus the number of transponders, capable of arriving simultaneously in the field of the analysis apparatus is no more than about ten.
By way of example, mention can be made of European patent application EP 0 285 419 which describes analysis apparatus for requiring a successive interrogations to determine an n-bit identity code.
Such analysis apparatus is unsuitable for the case where the identity code of each transponder is encoded on a large number of bits, e.g. 32 bits, and where a large number of transponders, e.g. more than 50, are present simultaneously in the field of the analysis apparatus.
Unfortunately this situation arises when transponders are used for remote identification of articles present in a container and for providing information concerning their origins, for example.
A particular object of the present invention is to enable a plurality of transponders to be identified in a relatively short length of time, for example to be able to determine how many of them there are, and to be able to address each of them separately to interrogate them.
The invention achieves this by a novel method of identifying a set of transponders situated in the field of analysis apparatus, each transponder having a different identity code in memory, the method being characterized by the fact that it comprises the steps consisting in:
a) causing the analysis apparatus to transmit data for comparison with a portion of the identity code as selected by the analysis apparatus;
b) causing each as-yet unidentified transponder to compare the received data and the portion of its identity code as selected by the analysis apparatus;
c) causing each as-yet unidentified transponder to transmit in at least one time window selected from a set of time windows common to the set of transponders as a function of the result of said comparison; and
d) causing the analysis apparatus to analyze the data transmitted by the transponders in said set of time windows, and when the data transmitted by the transponders does not enable a transponder identity code to be determined at least in part, causing the apparatus to start again with data that has been modified in such a manner that, within a finite number of iterations, the transponders are caused to transmit data enabling the identity code of at least one of the transponders to be determined, at least in part.
In a preferred implementation of the method, each transponder includes a comparison register in which the data for comparison is stored.
This comparison register is preferably organized to store a plurality of binary words, and the identity code is likewise made up of binary words.
In a preferred implementation of the invention, the analysis apparatus modifies, one at a time, a binary word of given significance in the comparison register, and each as-yet unidentified transponder compares the most-recently modified word with the binary word of corresponding significance of the identity code.
The portion of the identity code that is to be subjected to comparison is selected by selecting the significance of each new binary word that is to be stored in the comparison register.
Preferably, the method of the invention further comprises the step consisting in:
causing the analysis apparatus, whenever the data previously received thereby makes this possible to determine at least a portion of the identity code of one or more transponders to send an order causing said transponder(s) to transmit its/their identity code(s); and
analyzing said identity code(s) as received to determine whether only one identity code was transmitted or whether there has been interference associated with a plurality of different codes being transmitted simultaneously, and in the event of only one identity code being received, storing said code.
Results that are particularly satisfying in terms of the time required to identify all of the transponders have been obtained when the identification method comprises the steps consisting in;
a) using the analysis apparatus to transmit data to be compared with a portion of the identity code selected by the analysis apparatus;
b) within each unidentified transponder, comparing the received data and a corresponding portion of the transponder""s identity code;
c) causing each unidentified transponder to transmit in at least one time window selected from a set of time windows common to the set of transponders;
d) using the analysis apparatus to analyze the data transmitted by the transponders in said set of time windows, and when the data transmitted by the transponders does not enable at least part of the identity code of at least one of the transponders to be identified, beginning again with data modified in such a manner that, after a finite number of iterations, the transponders transmit data making it possible to determine at least a part of the identity code of at least one of the transponders:
e) causing the analysis apparatus, when the data previously received thereby makes it possible to determine at least a portion of the identity code of one or more transponders, to transmit an order causing every such transponder to transmit its own identity code; and
f) analyzing reception of the identity code to determine whether a single identity code has been transmitted or whether interference has occurred associated with simultaneous transmission of a plurality of different codes, and when only one identity code is received, storing said code.
Preferably, when a plurality of transponders transmit a plurality of different identity codes simultaneously and they interfere with one another, the method of the invention further includes the step consisting in sending new data to be compared with a new portion of the identity code in said transponders, other than the portion already determined by the analysis apparatus, optionally in modifying said new data until said new identity code portion has been determined, and thereafter in causing the transponder(s) for which the new identity code portion has been determined to transmit its/their identity code(s), and in the event of interference restarting the process for determining the identity code again by causing the comparison to be performed on an as-yet undetermined portion of the identity code, until only one identity code is received from the transponders.
In a preferred implementation of the method of the invention, each identified transponder is put into a standby mode in which it ceases to transmit the result of comparing its own identity code with the data transmitted by the analysis apparatus.
Preferably, each transponder that has been identified is put into said standby mode by using the analysis apparatus to transmit its identity code. The identity code is advantageously transmitted by loading said identity code into the comparison register, with the transponder whose comparison register matches its identity code then putting itself into a standby mode.
The invention also provides a transponder of the type comprising an identification code such as a serial number stored in a memory and means for remote communication with analysis apparatus, the transponder being characterized by the fact that it includes a comparison register in which data from the analysis apparatus can be stored, calculation means for comparing at least a portion of the identity code with at least a portion of the comparison register, and means for transmitting the result of the comparison in at least one time window selected from a set of time windows, the particular time window depending on the result of the comparison.
The invention also provides analysis apparatus for a plurality of transponders having different identity codes, the apparatus being characterized by the fact that it includes processor means organized to determine the identity codes of a plurality of transponders placed in the field of the analysis apparatus, said analysis apparatus being suitable for:
transmitting a write order associated with identity data, said order causing said identity data to be stored in the transponders at a particular address selected by the analysis apparatus;
analyzing the response from as-yet unidentified transponders in a set of time windows after said identity data has been transmitted;
transmitting a read order to cause the transponders whose identity codes have been determined in part to send their identity codes in full;
transmitting a new write order associated with new identity data in the event of interference between the data transmitted by the transponders, so as to end up by causing only one transponder at a time to send its identity code and storing said code; and
repeating the above steps so as to identity all of the transponders in turn.
The invention also provides analysis apparatus and a set of transponders for implementing a method as defined above.
By means of the invention, it is possible to identify a large number of transponders in a relatively short length of time, and to do so even if the identity code of each transponder is encoded on a large number of bits, e.g. 32 bits.